Cu-Sn alloys (bronzes) have been used in gearing and as a bearing material for many years. Gear applications use this material in the cast condition characterized by a relatively fine scale dendritic structure produced by chill casting centrifugally. In particular, double enveloping worm gears, utilized for many applications in which heavy shock loads are present or where limited backlash is desirable, are presently made from centrifugally cast phosphor gear bronzes. These bronzes generally consist of 9 to 12 w/o (weight percent) tin, up to 1.75 w/o nickel and the balance substantially copper. These alloys are often referred to as phosphor bronzes as a result of up to 0.25 w/o phosphorous being present from deoxidation during liquid metal processing.
Typical requirements for such a gear bronze include 310-345 Mpa (45-50 ksi) ultimate strength, 150-175 Mpa (22-25 ksi) yield strength, and 12% elongation to failure. Gears hobbed from such bronzes exhibit excellent wear resistance in lubricated sliding against steel.
The good wear characteristics of gears made from these gear bronzes have been attributed by some, but not all, researchers to the presence of relatively hard interdendritic phases which are embedded in a relatively tough and soft matrix of alpha phase (Cu-Sn solid solution). For example, it has been reported that increasing amounts of phosphorous in tin bronzes containing nominally 9.5 w/o tin was very effective in reducing the coefficient of friction and the wear rate in a pin on disc experiment. This work showed that increasing P contents (from 0-3 w/o) resulted in increasing amounts of the hard intermetallic Cu.sub.3 P phase which was responsible for increased overall hardness and improved wear properties. Tin should have a similar effect on increasing hardness and wear properties.
While this gear bronze does an adequate job in many applications, observations of worm gears used in service show failure occurring by a combination of cracking, pitting and/or spallation. There is thus a desire to reduce and retard the occurrence of these failures in service to prolong gear service life and also to increase the load capability, performance, and efficiency of these gear bronzes.
It is an object of the present invention to provide as-cast, age-hardened Cu-Sn-Ni worm gearing having improved strength and wear properties while retaining reasonable ductility.
It is another object of the present invention to provide a method of making as-cast, age-hardened Cu-Sn-Ni worm gearing having improved strength and wear properties.
It is another object of the present invention to provide such as-cast, age-hardened Cu-Sn-Ni worm gearing which is more resistant to failure in service (e.g., by cracking and/or gross surface degradation such as pitting, spallation and the like) and which improves the load capability of the worm gearing.